This is one area that seems to have a pretty unique set of circumstances for long travel offroad, which add compromises that make frequency play a less important role than other automotive environments. There were great discussions about frequency back on the old board like a decade ago, but a lot of it seems to have been thrown out the window (to a degree) for a much simpler overall recipe.
Basically what I hear these days if I were to try to throw an overgeneralized blanket statement onto long travel spring choices - (and please, anyone, correct me if i'm wrong or add more detail!) is that you basically try to set up shocks with ~1-2" of preload at full droop (because keeping smooth spring pressure all the way to the end seems significant, versus any sort of tender spring if the primary coils unseat), and the rate simply has to be soft enough to achieve your desired ride height. So if a truck has 10" of droop from ride height and 1,200lbs of sprung mass on that corner, you need a maximum primary wheel rate of 100lb/in (10"+2" of spring compression @ ride height). Then you can't go too much lower in primary rate before running into spring block height limitations (I believe?). So the window of useable spring rates that don't unseat and don't reach block height is pretty limited.
Now, it has been common to run dual rate setups with a step up collar that ramps the spring rate up to the value of the lower coil alone which does throw a wrench in the works as to how much energy is being stored by the springs (to be damped in rebound), but I recently saw note from
bdkw1 that it seems dual rate configurations are falling by the wayside (at least on big shocks) as things progress too. bdkw1, do you know if they are hitting block height on the upper spring on those single rate setups, or are they true single rate all the way to bump?
. Those are good times hah. I do have more questions about the context of the expected rebound forces you describe though, is that in the context of a vehicle with a multi-hundred lb/in wheel rate (spring rate @ the wheel) and minimal unsprung mass? If we shift to the context of a trophy truck with a sub-100lb/in wheel rate and more unsprung mass, it seems like the required rebound forces would be notably decreased? At least based on the much lower spring rate and in turn, less stored energy at full compression.
